WELLS OP LASALLE COUNTY, ILLINOIS. 637 



color and comparatively soft, being apparently of Wisconsin age. That 

 below the soil is of a brown or gray color and usually is rather hard. 

 Several gas wells have been obtained near the level of this old soil, as in 

 the neighboring portion of Bureau County, discussed above. Here, as in 

 Bureau County, the gas is probably largely derived from decomposition of 

 the vegetation in the buried soils and in the drift, but a portion may be 

 derived by escape from the underlying Trenton limestone. 



At Earlville, near the north border of the county, the public water 

 supply is from an 8-inch tubular well 150 feet in depth, which terminates 

 in limestone. The private wells in that vicinity are 30 to 60 feet in depth 

 and usually obtain water in gravel below till, though a few enter the rock. 1 



The public water supply at the city of Peru is obtained from an arte- 

 sian well 1,250 feet in depth, which terminates probably above the St. Peter 

 sandstone. Another well at the zinc works in Peru, 1,360 feet in depth, 

 obtains its supply from the St. Peter at the bottom and probably in part 

 from the limestones above this sandstone. The waterworks well is estimated 

 to have a capacity of 450 gallons per minute and its head is sufficient to 

 cause an overflow at 85 feet above the well mouth or 560 feet above tide. 

 An analysis of the water has been published in the Seventeenth Annual 

 Report of this Survey. 2 This analysis shows but 16 grains of sodium 

 chloride per gallon and the water is considered of excellent quality. There 

 is about 130 feet of drift in the Illinois Valley at this point. This gives 

 the rock floor an altitude but 330 feet above tide, which is fully as low as 

 at wells in this valley in Bureau and Putnam counties. This city seems to 

 stand a few miles east from the main preglacial valley. 



The city of Lasalle obtains its public water supply in part from springs 

 and in part from two artesian wells obtained in the Coal Measures sand- 

 stone at depths of 332 and 530 feet. The springs yield about 1,500,000 

 gallons a day and the wells about one-third that amount (C. H. Nicolet, 

 city engineer.) Many private wells are obtained in Lasalle at depths of 

 10 to 30 feet in gravel near the base of the drift. The Illinois River from 

 Lasalle eastward being outside the line of the preglacial valley, which it 

 enters west of this city, rock is found at comparatively slight depths in the 

 valley bottom. 



1 The flowing wells near Earlville are discussed in the Seventeenth Annual Report of this Survey 

 (Part II, pp. 779-780). 

 - Part II, p. 828. 



